1. Field of the Invention
The present invention relates to the field of high security locks and keyboards for the operation thereof.
2. Prior Art
High security locks of various kinds are well-known in the prior art. One type of such lock of particular interest to the present invention is keyboard operated locks wherein users of the lock are provided a code which, when entered into the keyboard, will operate the same. Such codes may be lock dependent, essentially serving as a combination for the lock, may be user dependent essentially identifying the user to the lock system, or may be a combination of lock and user dependent. An example of the first type of lock are locks controlling access to parts of a secure facility, whereas locks of the second type include those used as part of an automatic teller machine to enable function keys which allow one to withdraw money and conduct other transactions. In that regard, the words lock or locks as used herein are used in a general sense to denote a means for enabling an action which is otherwise disabled, such as the operation of a door latch or the withdrawal of funds in an automatic teller machine, or alternatively, the disabling of something which is normally enabled, such as might be required to lock something normally left unlocked.
In a conventional keyboard operated lock, the level of security attained is relatively low because the number to key assignments are fixed and ordered, and the sequence of key depressions of a user are normally observable from either side of the user without substantial difficulty. To alleviate this problem, and enhance the security of the overall system, keyboards are known wherein the keys are not given a predetermined and ordered 1-2-3 type sequence, but rather are given identifications just prior to use which identifications are effectively scrambled before the next such use. In this manner the physical key depression sequence observed during one operation of the system will have no meaning during the next operation of the system when the keys are identified differently. Further, in such systems the key identifications appearing when the user is standing in front of the keyboard are highly directional, and not observable from the side. Thus, the body of the user blocks the key identifications from view by others, so that while the physical key depressions can be observed from the side, the key identifications associated therewith cannot similarly be determined. Apparatus of this general type is disclosed in U.S. Pat. Nos. 4,644,326, 4,479,112 and 4,333,090. Also, another device having security features which include physical screening as well as mechanical and electronic realignment of numeric key entry functions is disclosed in U.S. Pat. No. 4,032,931.
The foregoing type of device provides high security as well as convenience, and is gaining increased popularity. However, in certain applications the full numeric keyboard may be more expensive than a particular market segment will support, or is larger than desired or required for a particular application, or both. By way of example, in the case of residential locks, a full numeric keyboard may cause the price of the lock to be too high to capture a large market. Also, on a door mounted lock, whether for residential use or otherwise, a full numeric keyboard may not fit conveniently on the door, particularly if one intended to mount the lock on a door already drilled or to be drilled for mounting a conventional lock set. Accordingly, it is to these general objectives that the present invention is directed.